Nudibranchs

Originally published August 19, 2009 (The Manitoban,Vol. 97, No. 3) 

Zoological Investigations

with your inevitably charming host, Mace Detective!

              Welcome, welcome, my literate learners, to the first in a series of exhilarating articles designed to delve into the wild and expansive realm of the lesser known and oft ignored members of kingdom Animalia. No stone will be left unturned as I, your journalistic host, solemnly vow to thrill your synapses with news of the humble exploits and existences of many contributors to life here on Earth.

 Today, I would like to draw your attention to the creatures known as nudibranchs. The word nudibranch means naked gills, in reference to the fact that nearly all of the nudibranchs have unprotected, external gills. Once grouped with the sea slugs, these amicable marine gastropod molluscs have recently been awarded the Linnaean distinction of being placed in their very own order, Nudibranchia. There are over 3000 species of nudibranchs grouped mainly as either Dorids or Eolids.    

 Nudibranchs are hermaphrodites, meaning that individuals possess both male and female reproductive organs. Mating nudibranchs engage in simultaneous, reciprocal reproduction where each fertilizes the other. Go ahead, take a moment to imagine that! They vary from 0.79 to 24 inches in length, are carnivorous, and usually venomous.

The Dorid nudibranchs feed mainly on poisonous sea sponges and can store the sponge’s toxins for use in their own self-defence. The Eolids frequently possess cerata—thin, tubular extensions of the digestive gland that run along the dorsal surface of their body. Members of this group have no gills, relying on gas exchange across the surface of their cerata, which are highly folded to increase the surface area available for this type of respiration.

Eolids feed primarily on Cnidarians such as jellyfish, anemones, and corals. Cnidarians possess defensive stinging cells, or nematocysts, which can inject extraordinarily painful poisons into all who stand in their way. Incredibly, Eolid nudibranchs have the ability to digest the stinging cells of their victims whole, passing the cells intact through the digestive gland to the surface of the cerata, where they are incorporated for use in the nudibranch’s own defense. Nematocystic theft!

Other nudibranch species have a symbiotic relationship with algae that live in the surface layers of their skin. The nudibranchs rely on the sugars produced by the algae during photosynthesis to meet their own dietary needs. Solar power!

One of the most exciting things about nudibranchs is their amazing, electric colouration and psychedelic patterning. Blazing blues, purples, reds, yellows, greens, whites and blacks; spots, stripes, swirls and decorative projections make these animals look like something out of a science fiction novel. These crazy molluscs are truly something wonderful—so check them out!